Binary stars and the UVX in early type galaxies

Abstract

We use the Hernández-Pérez $\&$ Bruzual (2013) HB13 stellar population synthesis models to study the rôle of interacting binary pairs as progenitors of EHB stars. We assemble a sample of 3417 Early Type Galaxies observed both in the optical (\textit{SDSS}-DR8) and the UV (\textit{GALEX}-GR6). The galaxies in our sample can be classified according to their position in the colour-colour diagram as UV weak or red sequence galaxies ($\sim 48\%$), UV strong or UVX galaxies ($\sim 9\%$), and recent star forming galaxies ($\sim 43\%$). Analysing this sample using the HB13 models for various choices of basic model parameters we conclude that: (a) The UV$r$ colours of UV weak and UV strong galaxies are reproduced by the models as long as the fraction of binary stars is at least 15$\%.$ (b) Higher metallicity models ($Z=0.02$ and $Z=0.03$) reproduce the colours of UV weak and UV strong galaxies better than lower $Z$ models. The $Z=0.03$ model is slightly bluer than the $Z=0.02$ model in the UV strong region, indicating a weak relationship between UVX and $Z$. (c) The strength of UVX increases with age in the model population. This is at variance with the results of other models that include binary stars as progenitors of EHB stars.

9 pages, 2 figures. Accepted to MNRAS

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Cited by in corpus (8)

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• Clues on the history of early-type galaxies from SDSS spectra and GALEX photometry
• The GALEX/S4G UV-IR color-color diagram: Catching spiral galaxies away from the Blue Sequence
• Galaxy And Mass Assembly (GAMA): Defining Passive Galaxy Samples and Searching for the UV Upturn
• The Ultraviolet Upturn in field Luminous Red Galaxies at $0.3<z<0.7$
• The effects of binary interactions on parameter determinations for early-type galaxies
• UV bright red-sequence galaxies: a comparative study between UV upturn and UV weak systems